Wang Yin, a 24-year-old graduate student at the elite Tsinghua University in Beijing, constantly uses Sina Weibo, China’s Twitter-like social networking site.
“On Weibo, I’m mostly interested in current events, what my friends are saying, and some information related to health and psychology,” Mr. Wang said. “Every day I log in over five times, using either my computer or mobile phone. And I stay on for two or three hours.”
Mr. Wang and Weibo’s 140 million other registered users are one big reason American Internet companies like Facebook, Twitter and YouTube want to get into China. It has the world’s biggest Internet population, about 457 million users, and they are mostly young people who spend long periods engaged in social networking, online games and electronic commerce.
But for now, they cannot enter China. Although there are no regulations that prevent American companies from operating here, the three popular American Web sites have been blocked in China for several years. Analysts say this is probably because the Chinese government wants to prevent the services from distributing uncensored information.
Meanwhile, the Chinese social networking companies are booming. Two weeks ago, shares of the Chinese social networking site Renren soared after a dazzling initial public offering on Wall Street that, for a time, gave the start-up a market value of close to $7 billion.
But Renren, despite being called China’s Facebook, is not even the leader of this country’s hottest Internet craze. That company is Sina.com, the 13-year-old online portal that has reinvented itself with Sina Weibo . Shares of Sina listed on the Nasdaq exchange have jumped about 250 percent during the last year, and some analysts estimate that the company’s microblog unit could alone be worth $5 billion.
It’s all about traffic. In the two years since microblog services became widely available in China, they have attracted more than 220 million registered users.
Now, as microblogs have a powerful effect on public discourse and advertisers start to create campaigns aimed at microblog users, other Chinese Internet companies are scrambling to develop and promote their own microblog services.
“This is a big, big category,” said Zhao Chunming, an Internet analyst at the Susquehanna International Group. “The news media and celebrities are tweeting; so are C.E.O.’s. This is changing the way people receive their news and information.”
What is striking is that microblog services are booming here despite a recent Chinese government crackdown on social networking sites in the wake of democracy demonstrations in North Africa and the Middle East. The restrictions, which typically involve deleting or censoring politically charged content, seem to be aimed at preventing microblogs and other sites from being used to foster dissent or organize antigovernment protests.
Still, young Internet users in China seem unfazed by the restrictions, in part because microblog services are a compelling alternative to this country’s more heavily censored state-run media and, perhaps more important, because microblogs are a powerful tool for self-expression.
“There are just so many talkative people on Weibo,” said Guobin Yang, an associate professor at Barnard College in New York and the author of “The Power of the Internet in China: Citizen Activism Online.” He said, “They talk about anything, from Marx and McLuhan to personal relationships and love affairs. So the real success of Weibo is that it offers a place for this kind of chitchat.”
American companies have not given up. Groupon, the online coupon giant, recently formed an alliance with Tencent , China’s biggest Internet company. And last December, Mark Zuckerberg, the founder of Facebook, visited Beijing and toured the offices of Sina and Baidu, China’s huge online search engine.
Facebook has dismissed rumors that it plans to enter China by teaming up with Baidu. Company executives have said only that they are exploring a way to enter China.
Analysts warn that the growth of Chinese microblogs could be curtailed if the government decided they have become too powerful a force in public opinion. But for the time being, microblog services are complying with censors and winning over new users, while social networking sites, like Renren, are struggling to keep pace, according to iResearch, an analytics firm based in Shanghai.
Some experts say the government may try to turn microblogs to its benefit, monitoring comments and traffic to take the pulse of the nation, and perhaps even anticipate and respond to signs of social discontent.
“It’s a real-time polling system to find out what’s going on in China,” said Bill Bishop, an independent Internet analyst in Beijing. “And it’s also a steam valve, since China’s a pressure cooker.” He says that if people get upset, “they can just say things on Weibo.”
Besides, analysts say, using Weibo — the Chinese word for microblog — is not about activism; it’s about free expression, sharing information and connecting with people in the know.
When Sina Weibo was introduced in 2009, the company built its microblog service by moving its most popular Internet bloggers — movie stars, real estate tycoons, athletes and writers — onto the microblog platform. Millions of young people soon followed.
Executives at Sina — who declined to be interviewed for this article — face intense competition from Tencent, Baidu and other microblog service providers.But for now, the company’s microblog service is the undisputed champion, partly because it got an early start but also because it combines features of both Twitter and Facebook, with some local elements thrown in.
Twitter, for example, does not allow users to post photographs and video, but Sina Weibo does. Sina also allows users to more effectively repost or comment on and share other people’s posts, creating bigger microblog communities.
Advertisers are flocking to microblogs, asking celebrities to promote their products or distributing coupons or promotions.
“My clients are saying, ‘Everybody’s on Weibo, so what do we do?’ ” said Peony Wu, chief digital officer at Ogilvy & Mather China. “So many big companies are now testing the waters.”